Embodiments of the present invention are generally directed towards video projection systems. Within the field of video projection, many systems using various imager technologies exist for projecting an image onto a viewing surface. By modulating the individual pixels on imager or micro-display device, light incident on the device can be manipulated to form high quality projected images. The form of light modulation varies based on the type of imager chip or micro-display used in the projection system. For example, imager chips can include transmissive, reflective and polarization switching pixels.
Transmissive systems, such as those based on liquid crystal device (LCD) type light valves, selectively transmit pixels by blocking light incident on one side of the imager based on the image data sent to the imager. Similarly, reflective systems, such as those based on digital micromirror device (DMD) and reflective LCD type imagers, selectively reflect light incident on the surface of the imager to form images. Polarization switching imager chips, such as LCOS based imagers, twist or phase shift the polarization of unpolarized or polarized light incident on imager chip and reflect the light through a polarization beam splitting optic to selectively form images.
Regardless of the type of imager chip, most projection systems are limited in their ability to produce a true black or dark pixel. This limitation is based on each type of imager's inability to completely stop light from leaking through or scattering off pixels that are in the “off” state. For example, the micromirrors on a DMD are not truly planar and even when an individual micromirror is angled to reflect the majority of light beyond a rejection angle of a total internal reflection (TIR) prism, some light is scattered onto an area of the viewing surface that is intended to be dark, thus reducing the ability of such projection systems to produce black or dark areas on the viewing surface. This problem is exacerbated when the imager is operated with contiguous regions of pixels in the “off-state” because the amount of scattered light from such regions can cause black areas to appear gray or less than dark.
The effect of gray regions in a projected image is particularly apparent in projection systems that use an imager chip with an area of operable pixels configured with a particular aspect ratio to produce a projected image of a different aspect ratio. In such systems, the entire operable area, i.e. all of the pixels of the imager, are illuminated using one or more light sources. To produce an image of an aspect ratio different from the native aspect ratio of imager chip, various regions of the imager chip can be maintained in “off” state or inactive mode to produce a dark border or frame around the projected image. However, because of the limitations of the most imager chips to produce a truly dark region anywhere on the screen, the border or frame can appear to be gray and thus reduce the overall perceived contrast ratio of the projected image.
For example, and imager chip with an operable area with a 16:9 aspect ratio can be used to project a Cinemascope image with a 2.35:1 aspect ratio by holding bands of “inactive pixels” at the top and bottom of the imager chip in the “off” state, while modulating the region of “active pixels” between the bands to produce the Cinemascope image. While the resulting Cinemascope image can be satisfactory for some applications, the visibility of the top and bottom bands due to leaked or scattered light from the non-active pixels can be distracting to viewers and reduce the perceived quality of the Cinemascope images.
Various embodiments of the present invention, alone and in combination, address these problems and can be used to improve the quality of projected video and images having an aspect ratio different from the aspect ratio of the imager chips used in projection system.